Re: [PATCH v1] ACPI / scan: Acquire device_hotplug_lock in acpi_scan_init()

David Hildenbrand
2019-07-26T08:06:03Z

On 26.07.19 09:57, Michal Hocko wrote:
> On Thu 25-07-19 22:49:36, David Hildenbrand wrote:
>> On 25.07.19 21:19, Michal Hocko wrote:
> [...]
>>> We need to rationalize the locking here, not to add more hacks.
>>
>> No, sorry. The real hack is calling a function that is *documented* to
>> be called under lock without it. That is an optimization for a special
>> case. That is the black magic in the code.
>
> OK, let me ask differently. What does the device_hotplug_lock actually
> protects from in the add_memory path? (Which data structures)
>
> This function is meant to be used when struct pages and node/zone data
> structures should be updated. Why should we even care about some device
> concept here? This should all be handled a layer up. Not all memory will
> have user space API to control online/offline state.

Via add_memory()/__add_memory() we create memory block devices for all
memory. So all memory we create via this function (IOW, hotplug) will
have user space APIs.

Sorry, I can't follow what you are saying here - are you confusing the
function we are talking about with arch_add_memory() ? (where I pulled
out the creation of memory block devices)

--

Thanks,

David / dhildenb